1. The four dimensional object behind the particle that has been subjected to wave function collapse. (by me)
Quantum decoherence. When a wave function appears to collapse it only does so in appearance. The wave is still existent "behind" the particle. That which is still globally existing behind the particle is the waveform.
Carl Sagan showed how a 3 dimensional world would look from a 2 dimensional perspective. If we look at the fourth dimension from the third dimension it will look much the same as the two dimension object looking at a third dimensional object and we will only see "parts" of what is actually there.